Gulgun Dede

Comparison of the Composting Performance of Four Different Sewage Sludge Amendments

ABSTRACT. High moisture content of sewage sludge is a major constraint in composting, and therefore sewage sludge needs to be mixed with bulking agents that have a high water absorption ratio and better structural stability. In this study, dewatered sludge has been mixed with four different bulking agents in terms of physicochemical properties, with a 1:1 (v/v) proportion of sawdust (SW), hazelnut husk (HH), corn straw (CS), or pine litter (PL), and the composting performances of bulking agents were investigated by considering temperature rise, CO2, H2S evolution, organic matter (OM) removal, C/N ratio, and dissolved organic carbon (DOC) removal. Three of the mixtures, namely, HH, PL, and SW, provided better initial composting conditions, ensuring an appropriate water–air balance within the compost matrix. CS was not able to supply sufficient porosity due to the smaller water absorption ratio and higher degradation rate, which induced anaerobic conditions. Among the mixtures, a higher and faster temperature rise (max 56.5°C) and CO2 release was provided by HH, while OM removal (53%) and DOC degradation were higher with the CS mixture, despite the low temperature rise and low peak value of CO2 release. Relatively low degradable carbonaceous contents of SW delayed all the composting indicators measured in the study. HH significantly enhanced bioreactions and accelerated the stability of sludge compost by providing both structural stability and a readily available carbon source, significantly shortening the composting time.

Effect of solarization on the removal of indicator microorganisms from municipal sewage sludge

The effect of solarization on bacterial inactivation in sewage sludge was studied using thermotolerant coliforms, enterococci and Escherichia coli (E. coli) as the indicator organisms. Solarization significantly increased the sludge temperature. The maximum temperatures were achieved at the beginning of the second week, reaching 65, 58, 55 and 50°C at depths of 0–10, 10–20, 20–30 and 30–40 cm, respectively. E. coli was found to be the most sensitive microorganism and was reduced to undetectable levels after 9 d at all monitored sludge depths. Thermotolerant coliforms were rapidly inactivated but were not reduced to below the detection limit. The inactivation curves of enterococci showed both shoulders and tailing, indicating a larger heat resistant fraction than with E. coli and the thermotolerant coliforms. Overall, the results suggest that the temperature regime produced by solarization was sufficient to reduce bacterial indicators to an acceptable level, meeting the pathogen regulation limit, in two weeks.

PHYSICOCHEMICAL CHARACTERIZATION OF HAZELNUT HUSK RESIDUES WITH DIFFERENT DECOMPOSITION DEGREES FOR SOILLESS GROWING MEDIA PREPARATION

In this study, the main physical, physiochemical, and chemical properties of hazelnut husk have been determined for the suitability as a container growing medium. Four substrates were prepared based upon decomposition degree: raw (H1), medium decomposed (H2, H3), and strongly decomposed hazelnut husk samples (H4), to determine the optimum growing medium parameters. Particle size was the key parameter to determine the physical properties, which was decreased with the increasing decomposition degrees. The main physical parameters were in the ranges for the ideal growing medium characteristics for H4. Except for raw material (H1), chemical characteristics such as pH, electrical conductivity (EC), carbon (C)/nitrogen (N), and nutrients were within acceptable ranges. The results indicated that hazelnut husk could be an alternative growing media component for containerized crops, if optimum particle size within the range of 0-2mm is obtained, for both aeration and water holding requirements.